In order to reduce the size of actuators and piezoelectric sensors, various piezoelectric thin-film elements including piezoelectric thin films have been proposed.
For example, Patent Document 1 described below discloses a piezoelectric thin-film element 1001 illustrated in FIG. 11.
The piezoelectric thin-film element 1001 includes a substrate 1002. On the substrate 1002, a lower electrode 1003, an underlying dielectric thin film 1004, a piezoelectric thin film 1005, and an upper electrode 1006 are stacked in this order. The piezoelectric thin-film element 1001 is produced in the following manner. On the substrate 1002 composed of Si, the lower electrode 1003 is formed by sputtering. On the lower electrode 1003, the underlying dielectric thin film 1004 composed of an alkaline niobium oxide represented by (Nax2Ky2Liz2)NbO3 (0≦x2≦1, 0≦y2≦1, 0≦z2≦1, x2+y2+z2=1) is then formed by sputtering at a substrate temperature of 650° C. Subsequently, on the underlying dielectric thin film 1004, the piezoelectric thin film 1005 composed of an alkaline niobium oxide represented by a general formula (Nax1Ky1Liz1)NbO3 (0≦x1≦1, 0≦y1≦1, 0≦z1≦1, x1+y1+z1=1) is then formed by sputtering at a substrate temperature of 650° C. On the piezoelectric thin film 1005, the upper electrode 1006 is then formed by sputtering.
The sodium composition proportions of the underlying dielectric thin film 1004 and the piezoelectric thin film 1005 are defined as 0<x2<x1.
In the formation of the piezoelectric thin film 1005 composed of an alkaline niobium oxide and in the formation of the underlying dielectric thin film 1004 composed of an alkaline niobium oxide and serving as an underlying film, the sodium composition proportions are different and hence targets having different compositions are used.